Re: Counting number of numbers in a large list between two valus

*To*: mathgroup at smc.vnet.net*Subject*: [mg114524] Re: Counting number of numbers in a large list between two valus*From*: Ray Koopman <koopman at sfu.ca>*Date*: Mon, 6 Dec 2010 06:15:05 -0500 (EST)*References*: <idhjda$9f6$1@smc.vnet.net>

On Dec 5, 6:56 pm, Lyle <lgor... at gmail.com> wrote: > Dear Listers, > > I have a large (5-20million) one dimensional list of real numbers and > I want to count the number of entries in the list that lie between 2 > specific values (x1, x2). I need to run the function for a number of > different ranges. > > ie. number of list entries (l), where x1 <= l <= x2 > > I've tried: > > tallydata[{x1_, x2_}] := Count[data, x_ /; x1 <= x <= x2] > > that takes about 3-4 seconds > > and > > tallydata[{x1_, x2_}] := Length[Select[data, x1 <= # <= x2 &]] > > which takes a little bit longer. > > The best I've managed is (this last one might be off by 1 or 2 but > this doesn't really matter to me): > > sorteddata = Sort[data]; > nf = Nearest[sorteddata]; > tallyrange[{x1_, x2_}] := > First[Position[sorteddata, First[nf[x2]]]] - > First[Position[sorteddata, First[nf[x1]]]] > > which takes between 1 and 2 seconds but I was hoping there might be a > faster way to do this? > > Any help would be great! > > Thanks, > Lyle Gordon > > Northwestern University data = RandomReal[1., 2*^6]; min = .2; max = .3; Timing@Length@Select[data, min <= # <= max &] {8.76, 200028} Timing@Count[data, x_ /; min <= x <= max] {7.99, 200028} Timing@Tr@UnitStep[(data - min)*(max - data)] {0.61, 200028}